Method of producing hot cathode tubes



y 1935- E. o. ERICKSON METHOD OF PRODUCING HQT CATHODE TUBES Filed May 10, 1952 J 2m n l l k i l ll: z/

Inventor Attorney! Patented May 28, 1935 4 g UNITED STATES PATENT OFFICE METHOD OF PRODUCING HOT CATHODE TUBES Ellis Osmon Erickson, Pasadena, Calii'., assignor to Claude Neon Electrical Products Corporation, Ltd., Wilmington, Del., a corporation of Delaware Application May 10, 1932, Serial No. 610,454

3 Claims. (Cl. 176-2) My invention relates to cathode discharge tubes, ing specifications, read in connection with the and has particular reference to a method of proaccompanying drawing, wherein the sole figure ducing such tubes to exhaust the tube and to actiis a diagrammatic view of a complete set up of vate the filaments thereof. apparatus required to process the tube in ac- 5 In the manufacturing of luminous tubular cordance with my invention. 5

lamps, particularly those employing one or more Referring to the drawing, I have illustrated hot cathodes, characterized in the final operating a luminous tube l of the hot cathode type which condition by a cathode fall of potential of the is to be employed with neon, argon, krypton, order of the ionizing potential of the gas emhelium, or other gas, or mixture of gases, which ployed, it hasbeen the practice to exhaust the will permit of operation with hot cathodes, such 10 tube while the tube is heated by some exterior tubes being known in the art as high intensity means for the purpose of driving off gases ocluminous tubes. Such tubes usually comprise a cluded in the material from which the tube or suitable envelope 2 which may be formed of glass, envelope is formed. The heating device has genquartz, or other suitable material having at each [5 erally consisted of an oven in which the entire end thereof electrodes, each of which comprises tube will be placed and brought to a relatively a filament 3 supported upon stems 4 and 5 high temperature while the exhausting is taking through which heating current may be conducted place. Such method is satisfactory for straight through the filament to cause the temperature of lengths of tubing of which great numbers are to the same to be raised to bring the filament up be made in a standard or substantially standard to high electron emission. Such tubes also em- 20 length. v ploy a ring 6, preferably surrounding the filament When the tube is to be formed in various shapes 3, which ring is used during the processing of and configurations, and of varying length, the the tube for the purpose of activating the filaconstruction of an oven which will be adapted for ment. The ring 6 is illustrated as being supvarious kinds and shapes of tubing becomes difliported upon a pair of stems 1' and 8, one of which 25 cult, and the use of such an oven becomes inconextends through the material of the envelope to venient and expensive. permit connection thereto of a suitable source of It is, therefore, an object of my invention to electrical energy during the step of activating provide a method of processing hot cathode tubes the filament.

in which the entire process may be carried on in The electrode at the opposite end of the tube 30 the open, giving a full view of the tube, and in is similarly constructed of a filament 9 mounted which the tube is accessible to the operator at all upon stems l0 and II, and the filament is surtimes and without discomfort to the operator. rounded by a ring I! mounted upon stems l3 and Another object of the invention is to provide a H, one of which, like the stem 8, extends through method of processing hot cathode tubes in which the envelope to permit electrical connection 35 the exhausting of the tube may be performed thereto. without an exterior source of heat. T In the manufacture of such tube, the central Another object of the invention is to provide elongated portion 15 of the envelope may be a method of processing hot cathode tubes in formed of the desired length and configuration,

which an electrical discharge is passed through while the end sections l6 and I! may be assem- 40 the tube while the pressure in the tube is at a low bled with their filaments and rings and then value and is employed for heating the tube. fused respectively to opposite ends of the cen- Another object of the invention is to provide tral section l5. An exhaust opening I8 is proa method of processing hot cathode tubes which vided permitting the exhausting of gases from are provided with a filament and activating ring within the completed envelope in finishing the 45 in which high potential is applied across the tube. rings to cause an electrical discharge therebe- The assembled envelope and, electrodes may tween to raise the temperature of the tube. then be placed upon a suitable table l9, or other Another object of the invention is to provide support, and a vacuum pump may be connected to a device for processing tubes in accordance with to the exhaust opening l8. When the air presr my invention which is adapted to process tubes sure within the tube reaches a point of about of varying shapes and sizes without alteration 5 m. m. the occluded gases within the material of any portion 01' the apparatus. of the envelope should be driven out and to ac- Other objects and advantages of my invencomplish this result each of the activating rings tion will be apparent from a study of the follow- 6 and I! may be respectively connected to oppo-.-

site terminals of a suitable source of high potential electric current. I

In the later steps of processing the tube suitable heating current must be supplied to the filaments '3 and 9, while direct current of relatively high potential must be applied to the activating rings and I2. I

I therefore provide a ready means for supplying various currents to the filaments of the electrodes through a multipole double-throw switch 20 connected in circuits which include a source of high potential alternating current (indicated by the legend 23000 V. A. C.) and also a suitable source of filament heating potential 28 for one of the filaments, a similar source of heating potential 22 for the other filament, also a source of direct current relatively high potential 23 for one of the electrodes, and another 2 3 for the other of the electrodes.

By referring to the drawing, it will be observed that each of the electrodes has provision for the connection of three electrical conductors, namely, to each of the stems t and 5 for the filaments 3 and stem 8 for the activating ring 6. The electrode at the opposite end of the tube is also provided for connection of three electrical conductors, respectively, to the filament stems 'l 0 and l l, and the activating ring stem M. It is, therefore,

. desirable to select the switch 20 with six poles,

one for each of the conductors required to lead to the tube i.

In order to facilitate the handling of the tube, I prefer to secure a terminal block 25 at some point adjacent the table E9, preferably at some suitable height above the table to which may be v 'connected a trio of flexible insulated conductors 26, 2'21 and 26. The conductor 2t is secured to of the switch 20 are thus connected to the activating rings t and I2, respectively. Hence, by connecting the source of high potential alternating current to corresponding terminals of the switch 20 on one side thereof, closing of the switch 20 against these terminals will connect a suitably controlled high potential source to the activating rings 6 and I2. Hence when the pressure within the tube has been reduced to a low value, such as 5 m. m., supplying high potential current to the rings 6 and I2, respectively, will cause an electrical discharge between these rings which will, in turn, cause a heating of the tube to any desired temperature. By regulating the current supplied to the rings with any suitable control apparatus (not shown), the heating of the tube may be regulated. The value of current employed may range from 350 to 400 milliamperes, though different values may be selected for different types of material of which the envelope is made and for different diameters of tubing to be treated. If desired, the gas pressure in the tube may also be suitably controlled to control the heating thereof.

I find that the best procedure includes that of initially supplying the high potential current for a short period of time until the glass, or other material of which the envelope is constructed, has warmed up slightly. Then the current should be cut off and air be permitted to enter the tube to again bring the pressure in the tube to atmospheric pressure. After this, the tube should again be exhausted to a low value, between 5 and 10 m. m. pressure. Then the discharge potential may again be placed upon the rings to heat the tube.

At this time it will be found that the air presminal Si is connected through a regulating rheostat N, to one pole of a high potential source of current 23. With the switch 20 in position to contact terminals 53, 55, 54, 60, GI and 62, the filaments 3 and 9 are respectively heated, while high direct current potential is placed upon the rings 8 and I2. A discharge will occur between the ring 6 and its associated filament 3 to cause activation of the filament 3, as is well known in the processing or activating of filaments or cathodes in vacuum tube operation by bombardment of the cathode by positive ions.

During the discharge between the filaments and their associated rings, a blue haze will occur about the rings and filaments, which, as activation is completed and high vacuum conditions are approached, will disappear accompanied by a reddening of the ring elements by bombardment upon its surface by electrons coming from the filament and now free to strike the rings with high kinetic energy by reason of the reduction in the number of gas particles present in the space which intervenes between filament and ring. The reduction in gas particles has resulted from the fact that the pump has been exhausting them and further because as the filament reaches complete activation, no further avolation of gases of decomposition of the coating takes place. Also, the gases occluded in the metal of the filament and ring have been effectively removed when both of those elements reach red heat. If it is desired, the ring elements can be heated further by radio frequency induction, as is also well known in the art. Then the pressure within the tube may be drawn down to any desired value, the proper amount of gas for producing the particular type of luminous tube desired being introduced to the tube, and the tube sealed, ready for use.

It will be observed that the rings 6 and I! are primarily used for the purpose of activating the filaments and these rings are common in the construction of cathode discharge tubes. My process employs these same rings for the purpose of heating the entire tube, rendering it unnecessary for the tube to be placdd in an oven or to be heated by any exterior device. Thus, irrespective of the shape or size of the tube, it may be readily treated without requiring any special construction of apparatus for various sizes and shapes of tubes. Moreover, the entire processing of the tube occurs while the tube is accessible to an operator and once the connections between the switch 20 and the terminal of the tube are made, it is unnecessary to further handle the tube, and each step of the process takes place under the eye of the operator, so that he may observe the condition of the tube at all times during the processing thereof, thus permitting a more ready production of uniform quality tubes.

My process of exhausting the tubes may also be applied to tubes designed for use with direct current in which one of the electrodes may be merely a plate or a carbon block, or similar device, in which case the electrode plate, block, or similar device, may be employed as the electrode at one end of the tube to which the high potential current may be supplied for the discharge of high potential current necessary for heating the tube.

Also, my process is adaptableto tubes having cathodes of types other than filament type, particularlyv since most of these tubes are supplied .with' electrode assemblies at'eachend'of the tube which include an electrode to be employed in the normal operation of the finished lamp, and also employs shielding rings or similar devices so that the shielding rings, if present, may be employed as electrodes for the high potential bombardment of the glass of the lamp for the purpose of heating the same.

In certain types of tubes, the electrode which is to be used in the normal operation of the tube may be of such construction that the passage of electric current, necessary for the heating of the tube, would destroy or injure the electrode for later normal operation. In this event, it may be necessary to add to the electrode assembly a suitable high potential electrode structure, such as the activating ring illustrated in this application. Such ring, however, will not only serve the purpose of conducting the high potential current for the heating of the-tube, but may also be formed about the normal electrode and be employed as a heat shield, if such shielding is later desired in the normal operation of the tube.

The activation process herein set forth is particularly adapted to rapid processing of tubes, particularly tubes of the character in which the time consumed in activating the cathode or filament is not considerably great. In certain instances, wherein large cathode surfaces areto be activated, or wherein the cathode surfaces are slow to activate, the time consumed in activating the filament will permit the glass of the lamp to cool oil to a considerable extent and thus the gases which might be occluded 'in the filament, and which may be produced by the chemical changes occurring in the cathode structure during activation, would tend to be absorbed by the now cooled glass. This condition may be avoided by passing high potential current between the electrode assemblies while the pressure within the tube is maintained ata relatively high value to thus heat the glass, as hereinbefore described, then activating the filament as hereinbeiore set forth, and then introducing into the tube a gas of such nature as will not chemically react with, or to poison, the now activated surface coatings of the electrodes to raise the pressure within the tube sufilciently to permit reheating of the glass upon passage of the high potential heating current.

Following this reheating of the glass, the tube is exhausted to high vacuum and the cathode parts are heated to drive off any occluded gases. Such parts as readily permit of such heating, such as filament type cathodes, are heated by supplying a heating current. Preferably, the positive ion bombardment of the cathode surfaces is reapplied to assist in their complete degassification. In general, the activating ring elements will become heated to a red heat by electron bombardment in the latter stages of the positive ion bombardment of the cathode surfaces, as was described before. Additiqnal heating of the ring elements can be produced by radio frequency induction, as is also well known in the art.

. Immediately upon the reheating of the glass with the inert or nonchemically active gas therein, the condition of a hot glass, and hot activated electrode, is obtained so that the tube maybe desired operating gases introduced into the tube.

and the same sealed off, thus completing the tube under the most favorable conditions.

While I have shown and described the preferred immediately evacuated to a high vacuum, thedescribed herein, except as defined in the appended claims.

I claim:

1. In a device for processing hot cathode vacuum tubes having a pair of spaced cathodes each with an activating electrode adjacent thereto, a source of high potential electric current, a separate source of heating current for each of said" cathodes, and a separate source of electrical potential for said activating electrodes, and means for selectively connecting said source of high potential in series relation with said activating electrodes and connecting said filaments and their activating electrodes, respectively, to their associated sources of current.

2. The method of processing hot cathode electrical discharge tubes having a coated cathode and having an activating electrode adjacent the cathode and another electrode at a point remote from the cathode which includes the steps of (1) applying'a high potential between the activating electrode and the remote electrode while maintaining sufiicient gas pressure in the tube to produce a discharge capable of heating the envelope of the tube to remove gas therefrom; (2) exhausting the tube to a very low pressure while applying potential between the cathode and its aooares adjacent activating electrode to activate the electrode; (3) introducing into the tube at sumcient pressure to support an envelope-heating discharge, a gas which is chemically inactive with respect to the activated cathode and again applying a high potential only between the activating electrode and the remote electrode to remove from the envelope any gas absorbed thereby during the activation of the cathode; (a) exhausting the tube while heating the cathode and activating electrode, and (5) introducing the desired operating gas and sealing ofl the tube.

3. In the method oi processing hot cathode electrical discharge tubes ha a coated cathode requiring activation and having an activati electrode adjacent the cathode and another electrode remote therefrom which includes the steps of (l) exhausting the tube and activating the cathode; (2) introducing into the tube at sumcient pressure to support an envelope-heating discharge, a gas that is inmtive with respect to the activated cathode and producing a discharge i: canton more 

